A depth from defocus (DFD) method has been proposed as a method for obtaining object distance information by using an image acquired by an image capturing apparatus, such as a digital camera, a digital video camera, a portable phone camera, a monitoring camera, and a medical camera.
The DFD method acquires a plurality of images with different amounts of blur by controlling image-acquisition parameters of a taking lens and so on. The method obtains the correlation among the amounts of blur of an area including surrounding pixels of each pixel and determines the object distance for each pixel with reference to prepared relationship between the correlation among the amounts of blur and object distances.
Japanese Patent Laid-Open No. 2010-016743 discloses calculating the correlation among the amounts of blur for each processing target area including a ranging target pixel in a plurality of images with different blurs acquired with different image-acquisition parameters to calculate an object distance from the correlation among the amounts of blur.
Japanese Patent Laid-Open No. 2007-043687 discloses a method for switching the apertures and the diameters of a camera at high speed.